1. Field of the Invention
This invention relates broadly to the coating of pipe, and more particularly to a method and means for coating pipe with cementitious material.
2. Description of the Prior Art
Pipes are often coated before being installed in order to provide certain qualities not possessed by the uncoated pipe. This is particularly true in the case of metal pipes, which are normally coated with asphalt or plastic material to protect against corrosion and are also sometimes coated with granular material to provide shock resistance. In addition, if the pipes are to be used in a wet environment, such as in river crossings and off-shore oil wells, or even in moist environments such as marshy grounds, they are normally coated with concrete to weight them down so as to protect against buoyancy or upward movement of the installed pipes.
When coating metal pipe with concrete, individual sections of pipe are normally coated by hand or by a sprayed fluid concrete mixture. In either case, the end portions of the pipe are left uncoated and are placed on end support stands to support the pipe section while the concrete is curing. After the coating is cured, the coated pipe sections are strung together on the pipe right-of-way and the pipe ends are welded together to form a continuous length of pipe. The uncoated end portions of the pipe sections are then also coated with concrete and, after curing, the pipe length is ready to be installed.
This procedure requires a great deal of time and can substantially delay the laying of the pipe line. Even if the application of concrete to the pipe lengths is carried out at the job site instead of at a plant or yard site, the double application of concrete to the pipe still extends the duration of the coating process. The coating procedure could obviously be shortened by coating the pipe in a single operation, but the prior art has not heretofore provided a way of accomplishing this. Although coating machines have been developed for applying asphalt and epoxy corrosion resistant materials to continuous lengths of pipe, the same concept has not been used to apply cementitious coatings to continuous lengths of metal pipe, presumably because of the unique problems involved in applying thick layers of cementitious material and the difficulty in supporting the coated pipe during the relatively long curing process without damaging the coating.
The choices offered, therefore, are to either coat the pipe sections individually in the slow conventional manner in order to allow the coating to cure prior to connecting the pipe in the field, or to coat the pipe after connecting the sections together, but only at the great risk, if not the certainty, of damaging the concrete coating while supporting the pipe as it is curing.
It would obviously be advantageous to be able to substantially shorten the cementitious coating process without adversely affecting the quality of the coated pipe for the reasons discussed above.